1. Field of the Invention
The present invention relates to an improved mill or rolling machine for use in the iron/steel industry and the non-iron field, and for producing a continuous strip of steel or the like with a desired thickness over the entire width by forcing a material to be rolled between a pair of work rollers or rolls. Further the present invention relates to an improved method of producing a strip using the above improved mill.
2. Description of the Related Art
A conventional 4-stage rolling machine or 4 high mill is schematically shown in FIGS. 8 to 11 attached hereto. In the figures, a pair of upper and lower work rollers or rolls 1 and 2 to be directly used for rolling the strip materials to a desired plate thickness are supported rotatably by work roller bearings of a chock type 15 and 16 respectively on both the ends. Both diameters of these upper work roller 1 and lower work roller 2 are usually invariable in an axial direction of work rollers 1 and 2.
A pair of overall upper and lower back-up rollers 3 and 4 usually having a crown shape as shown in FIG. 13a (the diameter of central portion of back-up rollers 3 and 4 is larger and the diameter becomes smaller at both ends) are supported rotatably by the back-up roller bearings 17 and 18 respectively in the manner of sandwiching said pair of upper and lower work rollers 1 and 2. Further, the diameter of afore-mentioned upper and lower back-up rollers 3 and 4 is designed to be larger than the diameter of upper and lower work rollers 1 and 2, and both pairs of the overall back-up rollers 3 and 4 or of work rollers 1 and 2 usually have the same diameter. The above conventional back-up roller or roll may be called "an overall back-up roller", since it has a backing-up effect overall on a corresponding work roller. When pressure oil has been introduced into a milling or rolling cylinder or ram 8, so called "push-up ram" installed inside the housing 10 from the pressure oil supplying unit that is not shown in the figure, the lower back-up roller bearing of a chock type 18 at both ends of lower back-up roller 4 is pressed upward as shown in FIG. 10. The push pressure P from this lower back-up roller 4 is transmitted to the lower work roller 2 of small diameter which comes in contact with each other and turns in the opposite direction and becomes the rolling force against plate material 5 inserted between the upper and lower work rollers 1 and 2.
Further, by the reaction force R during the rolling of plate material 5 being inserted between the upper and lower work rollers 1 and 2, the upper work roller 1 is apt to be bent to a convex shape while the lower work roller 2 is bent to a concave shape. These reaction forces R hold a pair of upper and lower work rollers 1 and 2 from both the upper and lower sides and are transmitted to the back-up rollers 3 and 4 which turn in opposite direction and are in contact with each other, while the back-up rollers 3 and 4 are larger in diameter and stronger in rigidity than the work rollers 1 and 2, so the reaction forces R being transmitted from the work rollers 1 and 2 are alleviated. As shown in FIG. 12 during this rolling, there appears the difference in thickness (H-h) between the thickness "h" of end portion of plate material 5 and the thickness "H" of central portion, and in the cross sectional view that has been cut in the direction perpendicular to the feed direction of plate material 5, the upper/lower shapes of strip material 5a rolled and coming out between the upper and lower work rollers 1 and 2 are not flat, or are apt to be rolled to the strip material 5a of so-called edge waved shape where the thickness at the central portion of strip material 5a becomes thicker while both the ends become thinner.
A variety of proposals are being presented so that the upper/lower faces of the plate can be rolled flat while the resultant strip material can be prevented from attaining an edge-waved shape.
One is the method called a roller bending method where a bending cylinder is installed at the roller neck. This technique is mainly applied to such a 4 stage rolling machine and is used to forcedly bend the work roller by the external force to change the roller crown. This method is applicable in the work roller bending method and the back-up roller bending method.
There is also another technique named the VC roller method wherein an oil chamber is laid out inside the rolling roller and the oil pressure acting therein is adjusted for changing the crown of the work roller.
In addition to them, there is the heat crown method for thermally expanding a part of the work roller to change the crown, and there is the roll coolant method for theremally reducing a part of the work roll diameter by adjusting a coolant volume. The above mentioned roller bending technique is the method rich in conformity and contains a certain degree of flexibility as described above, but because the work roller is restricted to the entire face of the back-up roller as shown in FIG. 13(a) and FIG. 13(b), it is difficult to provide a sufficient deflection to the work roller and not only lacks in absolute capability but the back-up roller needs to be changed in view of the width, strength, shape and the like of plate material for changing the crown of the back-up roller. Further, the VC method is expensive due to the cost of the back-up roller. Its maintenance is also troublesome.
In addition, the heat crown method and the roll coolant method involve a great problem in that its responsibility is poor, though both methods are very flexible.
Further, in the above 4-stage rolling machine, it is noted that there is a limit to its shape controlling function, and it was difficult to say that said machine was sufficiently effective in controlling against edge drop where the wall thickness on the side edge portions of rolled material 5 decreased continuously. For this reason, in order to enhance the shape controlling and crown controlling effects, a 6-stage rolling machine or 6-high mill has been proposed and has been actually used (JP Unexamined Patent Publication No. 47 (1972)--29,260). This machine tries to adjust the distribution of rolling forces for enhancing the shape correcting function by arranging the intermediate rollers 6 and 6' between work rollers 1 and 2 and overall back-up rollers 3 and 4 as shown in FIG. 14. And such a technique also proposes that the counterplan controlling against edge drop becomes effective by adjusting the roller bending force and the shift distances of intermediate rollers 6 and 6' (JP Examined Patent Publication No. 56 (1981)--14,362).
However, in the said conventional rolling machine, there are such defects that it is difficult to give a sufficient roller bending force to the work rollers because the work rollers 1 and 2 and the intermediate rollers 6 and 6' are constrained by almost all the entire faces of back-up rollers 3 and 4, and that not only the said machine is lacking in absolute shape control capability but the back-up roller also needs to be re-assembled for changing the crown shape in view of the plate width, strength, shape and the like of rolled material especially in a 4-stage rolling machine. In addition, because the shift direction by intermediate roller is limited to a single direction in the conventional 6-stage rolling machine, an undulation along the plate width direction of rolled material sometimes appears even after the enforcement of the crown control, and it is difficult to obtain a sufficient shape controlling function in the said machine. Still more, because the back-up rollers turning in contact with the work rollers and intermediate rollers are in contact with almost all the entire faces, it is impossible to optionally change the back-up fulcrum and to control the shape at an optional position. In addition, the back-up rollers need to be ground on their entire faces and a sufficient space is required at the side of the rolling machine because of the difficulty in maintenance and the shift mechanism of the intermediate rollers.